Which soil type is described as least stable and often non-cohesive?

• A. Type A
• B. Type B
• C. Type C
• D. Type D

Answer: (C)

Soil stability depends on two main properties: cohesion, which is the sticking together of particles, and internal friction, which resists sliding between particles. Non-cohesive soils have little to no bonding between grains, so they rely almost entirely on friction for strength. This makes them prone to rearranging or sliding under loads, especially when they’re saturated with water, leading to lower shear strength and a higher tendency for failure. Because of this lack of bonding, non-cohesive soils are generally the least stable among common soil types. The option describing a non-cohesive soil matches this behavior, so it’s the best choice.